1. Field of the Invention
The present invention relates generally to a method of transforming informations derived from color sensation informations sensed by living bodies (hereinafter referred to simply as color sensation informations) and an apparatus for carrying out the foregoing method. More particularly, the present invention relates to a method and an apparatus for processing color sensation informations such that informations given in the form of physical quantities are transformed into psychological quantities each representing a certain color sensed by living bodies and vice versa in order to assure that the apparatus can be utilized as a color sensor and, moreover, the apparatus can be utilized in many industrial fields associated with printing, building, dressing and so forth.
2. Description of the Prior Art
When it is required that a color possessed by a certain substance is exactly specified in many fields associated with printing, building, dressing and others, the color is generally represented by a mark or a numeral. For example, with respect to an unit for processing color informations, three primary colors (comprising a red (R), a green (G) and a blue (B)) inputted from a scanner or a camera to represent a certain color or a three-dimensional coordinate (i.e., a color representing system including X-, Y- and Z-coordinate axes) identified by a linear combination of the three primary colors are used. In addition, an operation such as color modification, color transformation or the like is performed by using marks and/or numerals.
On the other hand, a Munsel color system is one of color representing systems to be used when it is required that a color possessed by a certain substance is exactly specified in many fields associated with printing, building, dressing and others. The Munsel color system is built based on color sensation of a human being such that all colors possessed by substances are arranged in a three-dimensional space with three properties of lightness (V), Hue (H) and chroma (C) as a scale in order that each of the colors is identified by marks and/or numerals (see FIG. 6).
Specifically, with respect to achromatic colors in the Munsel color system, variation of brightness values ranging from black to white are represented by actual numerals ranging from 0 to 10 such that a quantity of variation of the brightness value corresponding to one calibration is equally sensed by eyes of a human being. On the other hand, with respect to chromatic colors in the Munsel color system, the same lightness of a certain chromatic color sensed by a human being as that of a certain achromatic color is referred to as a lightness of the chromatic color. .theta. of a polar coordinate (r, .theta.) on the equilightness plane represents a hue and r of the same represents a chroma (see FIG. 5). Concretely, every hue is divided into a group of colors located adjacent to each other in accordance of an order of 10 colors, i.e., R (red), YR (yellowish red), Y (yellow), GY (greenish yellow), G (green), BG (blueish green), B (blue), PB (blueish purple), P (purple) and RP (redish purple). In addition a circumference of 360 degrees is divided into 10 sections such that a group of colors is annularly arranged along the circumference including ten sections and color phases in the group of colors are represented by calibrations of real numerals ranging from 0 to 10. Thus, every hue is arranged such that they vary continuously in the region covering one group of colors as well as in the boundary between one group of colors and the adjacent group of colors so that a quantity of variation corresponding to one calibration is equally sensed by a human being at all locations. On the other hand, with respect to the chroma, an achromatic color is represented by 0 and a most lightness color is represented by 16 so that all the chromas are represented by a calibration corresponding to one of actual numerals of 0 to 16. Thus, a quantity of variation of a chroma corresponding to one calibration between different hue is equally sensed by a human being.
Therefore, with respect to a certain single property, a distance between two points in the foregoing space (i.e., Munsel color space) is determined in proportion to the sensitive difference between two points associated with the relevant property.
In the Munsel color system, e.g., designation of 10RP7/8 represents that the hue (Hue) is equal to 10 RP, the lightness (Value) is equal to 7 and the chroma (Chroma) is equal to 8. In this manner, a standard color chart is issued to each color of which coordinate is represented by an integral in the same way as the aforementioned example. However, with respect to a color of which coordinate is not represented by an integral, the color can be detected in the form of an image by the sensation of a human being via interpolation based on the standard color chart.
It has been known as an important thing that the foregoing color system can be obtained merely by linear combination of the aforementioned primary three colors (R, G, B).
As will be apparent from the above description, the Munsel color system provides a method of representing a color in conformity with color sensation of a human being and has an advantage that its structural mechanism can readily be understood and recognized by an ordinary person.
However, it is certain that the color charts can readily be understood and recognized by an ordinary person but they have a drawback in that they can not serve as an invariable scale for indicating each color because they vary due to undersirable deterioration of pigment contained in each color chart or the like substance as time elapses. In fact, this problem has been solved by represneting each color using its physical properties.
Spectral distribution represented by a spectral reflectance, a spectral transparency or the like is one of the foregoing physical properties inherent to each color. Specifically, with respect to a component spectrum at each wavelength of standard illumination, such a rate that the standard illumination is reflected at the surface of a substance or penetrates through a medium when standard illumination is radiated to the surface of the substance or through the medium varies depending on the kind of a color of the substance but does not vary with a same color. The functions representing a wavelength .lambda. specific to each color is called a spectral reflectance function or a spectral transparency function, and a spectrophotometer for measuring a value derived from each function at the wavelength .lambda. has been heretofore known.
Although distribution of spectral intensity is a physical value and therefore it is an objective value, it is difficult for an ordinary person to detect a certain color in the form of an image based on the foregoing value.
A spectrophotometer for measuring distribution of spectral intensity and then displaying it in X-, Y- and Z-coordinates in view of the aforementioned fact has been heretofore known.
As in the case of representation of the three properties, representation in X-, Y- and Z-coordinates belongs to a method of arranging colors in a three-dimensional space. The coordinates employed for the purpose of representation provide artificial values derived upon arithmetic processing as three primary colors of their linear combination based on the distribution of spectral intensity in the above-described manner. On the other hand, with respect to a visual neural system of a human being, it has been known that multidimensional physical data are non-linearly transformed into a lower dimensional space, and color sensation is accomplished based on the foregoing non-linear transformation. However, since a distance between two points in the color space including X-, Y- and Z-coordinates is not determined in proportion to the sensitivity of a human being, it is very difficult for a color having no color chart to be detected in the form of an image by interpolation. For this reason, there arises a problem that a color operation or the like performed by using the conventional linear combination of the three primary colors, i.e., R, G and B is slightly deviated from the sensation of a human being.